html, body {
  margin:0;
  min-height: 100vh;
  height: 100vh;


}
body {
  margin:0;
  display: flex;
  flex-direction: column;
  min-height: 100vh;
  height: 100vh;
}
header {
  order: 1;
  flex-shrink: 0;
  flex-basis: 50px;
  background:red;
}
article {
  order: 2;
  overflow-y: scroll;
  background:green;
  flex-grow: 1;
}
footer {
  order: 3;
  flex-basis: 50px;
  min-height:50px;
  background:blue;
}

#ground1{
 width:512px;
 height:512px;
}